UNHCR's Regional Refugee Coordinator for the Refugee Crisis in Europe Vincent Cochetel attends a news briefing at the United Nations European headquarters in Geneva, Switzerland, March 8, 2016. REUTERS/Denis Balibouse

GENEVA (Reuters) - The United Nations’ refugee agency said on Tuesday proposals to send back refugees en masse from the European Union to Turkey would contravene their right to protection under European and international law.

Turkey offered on Monday to take back all migrants who cross into Europe from its soil in return for more money, faster EU membership talks and quicker visa-free travel for Turks. EU leaders accepted the offer in principle.

“The collective expulsion of foreigners is prohibited under the European Convention of Human Rights,” Vincent Cochetel, Europe regional director of the U.N. High Commissioner for Refugees (UNHCR), told a news briefing in Geneva.

“An agreement that would be tantamount to a blanket return of any foreigners to a third country is not consistent with European law, is not consistent with international law.”

Cochetel said nine in 10 of those arriving in Europe each day were Syrians, Iraqis and Afghanis “fleeing for their life” who deserved international protection.

Europe’s commitment to resettle 20,000 refugees over two years, on a voluntary basis, remains “very low”, he said.

Europe had not even fulfilled its agreement last September to relocate 66,000 refugees from Greece, redistributing only 600 to date within the 28-nation bloc, Cochetel said.

“What didn’t happen from Greece, will it happen from Turkey? We’ll see, I have some doubts,” he said on Swiss radio RTS.

Turkey is hosting nearly 3 million Syrian refugees, the most worldwide, and has “done more than all the EU countries together”, he said. But its acceptance rate for refugees from Afghanistan, Iraq and Iran is “very low”, at about 3 percent, Cochetel said.

“BALANCED AGREEMENT” NEEDED

“We hope that the EU member states and Turkey will come up with a balanced agreement and that this balanced agreement won’t be to the detriment of people seeking international protection.”

Before an EU summit on March 17, “supplementary guarantees” must be put in place so those sent back to Turkey will have their asylum requests reviewed, he said.

The U.N. Children’s Fund also voiced deep concerns about the migrant plan, noting that 40 percent of refugees were under 18.

“The fundamental principle of ‘do no harm’ must apply every step of the way,” UNICEF spokeswoman Sarah Crowe said.

“That means first and foremost that children’s rights to claim international protection must be guaranteed. Children should not to be returned if they face risks including detention, forced recruitment, trafficking or exploitation.”